The Applicant has developed a wide range of printers that employ pagewidth printheads instead of traditional reciprocating printhead designs. Pagewidth designs increase print speeds as the printhead does not traverse back and forth across the page to deposit a line of an image. The pagewidth printhead simply deposits the ink on the media as it moves past at high speeds. Such printheads have made it possible to perform full colour 1600 dpi printing at speeds in the vicinity of 60 pages per minute; speeds previously unattainable with conventional inkjet printers.
Printing at these speeds consumes ink quickly and this gives rise to problems with supplying the printhead with enough ink. Not only are the flow rates higher but distributing the ink along the entire length of a pagewidth printhead is more complex than feeding ink to a relatively small reciprocating printhead.
The high print speeds require a large ink supply flow rate. This mass of ink is moving relatively quickly through the supply line. Abruptly ending a print job, or simply at the end of a printed page, means that this relatively high volume of ink that is flowing relatively quickly must also come to an immediate stop. However, suddenly arresting the ink momentum gives rise to a pressure pulse in the ink line. The components making up the printhead are typically stiff and provide almost no flex as the column of ink in the line is brought to rest. Without any compliance in the ink line, the pressure spike can exceed the Laplace pressure (the pressure provided by the surface tension of the ink at the nozzles openings to retain ink in the nozzle chambers) and flood the front surface of the printhead nozzles. If the nozzles flood, ink may not eject and artifacts appear in the printing.
Resonant standing waves in the ink occur when the nozzle firing pattern matches a resonant frequency of the ink supply line. Again, because of the stiff structures that define the ink line, a large proportion of nozzles for one color, firing simultaneously, can create a standing wave in the ink line. For example, printing spaced black lines for, say, a table of data, will fire many, if not most, of the black nozzles at a particular frequency. If this particular frequency matches a resonant frequency of the ink supply structure, a standing wave can start oscillating back and forth. This can result in nozzle flooding, or conversely nozzle deprime because of the sudden pressure drop after the spike, if the Laplace pressure is exceeded.
The Applicant has addressed these issues by incorporating non-priming cavities into the printhead. A detailed description of the non-priming cavities is provided in the Applicant's co-pending U.S. Ser. No. 11/688,863, the contents of which is incorporated herein by reference. Briefly, the stiff structures that define the ink line have air pockets distributed long the length of the printhead. A pressure pulse from a resonant standing wave in the ink will compress the air in the cavity as it passes that point in the ink line. Compressing the air in the cavity damps and dissipates the pressure pulse. The reduced pulse amplitude is less likely to flood the nozzles.
Unfortunately, the lowest resonant frequencies of the ink line have the highest pressure amplitudes. To damp these pressure waves, the non-priming cavities need to be impractically large. A series of large air pockets positioned along the ink line is counter to compact design. Furthermore, diurnal heating and cooling of big air cavities would either pump a large volume of ink out through the nozzles, or deprime the nozzles by drawing ink back into the support molding.